Intelligent Transport Systems (ITS) are systems that sense, gather and communicate data in a transportation setting. The aim of such systems is to aid transportation systems to operate more safely, efficiently or cost effectively, and to aid in the planning and management of transportation systems. Exemplary uses of ITS include traffic flow monitoring, variable tolling, emergency vehicle tracking and deployment and dynamic traffic control, to name a few.
Some components of ITS are affixed to moving vehicles. These devices communicate with each other and/or fixed components of the system wirelessly. ITS typically operate at 5.9 GHz, and may be compliant with draft standards such as ETSI TS 202 663 or IEEE 1609/802.11p for example.
However, one potential issue for deployment of ITS is the requirement of coexistence between the already deployed Road Transport and Traffic Telematics (RTTT) Dedicated Short Range Communication (DSRC) devices and other similar systems and ITS devices.
RTTT-DSRC devices include systems that are used to collect road tolls, such as the system illustrated in FIG. 1. These devices typically operate at 5.8 GHz.
The RTTT-DSRC system of FIG. 1 includes road side equipment (RSE) 102 and one or more RTTT-DSRC devices 104, 104A, such as those carried by vehicles 106, 106A. Typically RTTT-DSRC devices 104 are low power devices capable of running off batteries for long periods. The device 104 operates in a very low power mode listening for signals from road side equipment 102 (e.g. a toll gantry). When the RTTT-DSRC device 104 “hears” a signal it “wakes up” and enters a higher power mode and attempts to execute a transaction with the RSE 102. The wireless connectivity range for RTTT-DSRC devices 104, 104A is typically short, say less than 100 m. The RTTT-DSRC will only operate over the zone 108 in which it is capable of communicating with the RSE 102 as the vehicle 106 moves past it. Thus, in FIG. 1 the RTTT-DSRC device 104 can communicate with the RSE 102, but RTTT-DSRC device 104A is out of range.
On the other hand, ITS devices can have higher transmit powers and may be active continuously. In FIG. 1 each vehicle 106, 106A has an ITS device 110, 110A affixed to them.
FIG. 2 is a schematic block diagram of the ITS device 110. The device 110 has an ITS radio component 204 which is effectively the physical transmitter and receiver of the device 110. Operation of the device 110 is controlled via a manager component 202, and it runs a protocol stack 206. As noted above the device 110 will typically operate on a channel at 5.9 GHz, and will be compliant with draft standards such as ETSI TS 202 663 or IEEE 1609/802.11p for example.
Despite the fact that they operate at slightly different carrier frequencies, interference can result between the systems. Interference has the potential to disrupt communication via the RTTT-DSRC.
It is thus desirable to have ITS devices avoid causing interference around RTTT-DSRC signalling zones. To date several solutions have been proposed for this problem:                The RSE can be fitted with an ITS radio device. This ITS radio device transmits a message, the reception of which by a vehicle's ITS device indicates that the vehicle's receiver is in the vicinity of a RTTT-DSRC zone. The message can include a message type indicating that this message is to be interpreted as transmitted from a RTTT-DSRC location. The vehicle's ITS receiver may then determine that it is in a RTTT-DSRC zone simply because it received a message of this type. The message may also include the position of the gantry. This is helpful if the vehicle's ITS device is position aware, e.g. if it has GPS positioning capabilities or across to GPS data from another source. If the vehicle is told where the RTTT-DSRC zone is and it knows its own location in the same co-ordinate system then it can determine whether or not it is in the RTTT-DSRC zone. The dimensions of the RTTT-DSRC zone can also be included in the message transmitted by the RSE's ITS radio. The message could also include authentication data to validate the message as a countermeasure to spoofing attacks aimed at ITS devices.        The vehicle's ITS device can be provided with means for receiving RTTT-DSRC signals. The ITS device can then receive RTTT-DSRC signals. The reception of the DSRC signal would indicate to the ITS device that it is in the vicinity of a RTTT-DSRC zone. The reception means includes a dedicated hardware subsystem, radio equipment able to receive and decode the DSRC signal. This subsystem is connected to the ITS device management system which can suspend ITS transmission when the RTT DSRC radio system indicates that it is in a RTTT-DSRC zone.        
It is an object of the present invention to provide an alternative mechanism to avoid interference between an ITS device and other radio systems such as RTTT-DSRC systems.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.